Purifying sulfonic acids



Patented Aug. 15, 1950 PURIFYING SULFONIC ACIDS Wayne A. Proell, Chicago, 111., assignor to StandardOil Company, Chicago, 111., a corporation of Indiana No Drawing. Application November 19, 1948, Serial No. 61,135

16 Claims. ((21.260-513) This invention relates to a process for purifying crude sulfonic acids containing oxidizing impurities, particularly sulfuric acid, nitric acid, nitrogen oxides andthe like. In another aspect, this invention is concerned with a process .for the distillation of crude sulfonic acids under low pressure, which distillation process is preceded by treatment of the crude sulfonic acids with a material affording Has to react with and remove oxidizing impurities contained in said crude sulfonic acids which would otherwise interfere with their low pressure distillation.

Although numerous processes are known for the preparation of sulfonic acids, many of the processes in commercial use or potentially available suiier the disadvantage of producing sulfonic acids containing oxidizing impurities, particularly sulfuric acid or nitric acid and nitrogen oxides. Thus, the sulfonic acids, particularly aikanesulfonic acids having 1 to 5 carbon atoms, inclusive, in the molecule, produced by nitrogen oxide catalyzed oxidation of disulfides (U. S. Patents 2,433,395-6 and U. S. Patent 2,505,910 of W. A. Proell and B. H. Shoemaker, patented May 2, 1950) and the like contain small but significant proportions of sulfuric acid and nitric acid or nitrogen oxides which, as will be pointed out in more detail hereinafter, tend to interfere with the employment of these acids for certain pur-* poses. Similarly, the reaction of concentrated or fuming sulfuric acid or S03 with hydrocarbons yields reaction products containing substantial proportions of sulfuric acid as a contaminant, even though liming out or similar procedures are used to reduce the proportion of sulfuric acid in the sulfonic acid products. Thus, technical benzenesulfonic acid may contain as much as 25 percent of sulfuric acid and technical toluene sulfonic acid as much as 8 percent of sulfuric acid. Similarly, the well known process of oxidizing hydrocarbon disulfides with concentrated or fuming nitric acid yields products more or less contaminated with sulfuric acid, nitric acid and or nitrogen oxides.

The presence of oxidizing impurities in crude sulfonic acids is highly undesirable. Thus when the sulfonic acid is intended for use as an addition agent or electrolyte in electroplating baths, the presence of sulfuric acid as an'impurity leads to the formation of insoluble heavy metal sulfate precipitates in the plating baths. Sulfuric acid is an undesirable impurity in sulfonic acids, particularly alkanesulfonic acids having 1' to 5 car:- bon atoms, inclusive, in the alkyl group, employed as solventsand catalystsfor the esterification of 2 cellulose with fatty acids, particularly acetic acid, since this impurity tends to cause darkening and charring of the cellulose.

I have also observed that the presence of oxidizing impurities such as sulfuric acid, nitric acid and/or nitrogen oxides in distillable sulfonic acids, particularly alkanesulfonic acids having 1 to 5 carbon atoms, inclusive, in the alkyl group, tends to induce substantial gas evolution during the low pressure distillation of said sulfonic acids, thereby seriously reducing the maximum rate of distillation and necessitating the use of larger vacuum pumps than would otherwise be necessary. Since low pressure distillation is an essential purification step in the manufacture of certain sulfonic acids for a number of uses, the provision of an eflicacious process for the removal of oxidizing and gas-evolving impurities from such sulfonic acids is of technical and commercial importance.

It is an object of this invention to provide a process for the removal of oxidizing impurities from crude sulfonic acids containing the same. Another object of this invention is to provide a process for reducing or eliminating sulfuric acid contained as an impurity in sulfonic acids. An additional object of this invention is to provide a process for the removal of oxidizing impurities such as sulfuric acid, nitric acid and nitrogen oxides from alkanesulfonic acids having 1 to 5 carbon atoms, inclusive, in the alkyl group. Still another object of this invention is to provide a unitary process for the purification of alkanesulfonic acids having 1 to 5 carbon atoms, inclusive, in the alkyl group and containing sulfuric acid as an impurity, which process comprises a reducing treatment with hydrogen sulfide, separation of resultant solid reaction products from the reaction mixture and distillation of the sulfonic acid thus treated under a low (subatmospheric) pressure. These and other ob- ,iects ofv my invention will become apparent from the ensuing description thereof.

' My invention finds particular application to crude alkanesulfonic acids having 1 to 5 carbon atoms, inclusive, in the alkyl group, containing between about and about weight percent sulfonic acid, between about 1 and about 5 weight percent sulfuric acid and between about 1 and about 10 weight percent of water. a

The following table presents illustrative data concerning the composition of various low molecular weight alkanesulfonic acids producedby the Oxidation of alkyl disulfides with an oxygencontaining gas and a nitrogen oxide or nitric acid catalyst.

In accordance with the process Of this invention the sulfuric acid and, optionally, other oxidizing materials contained in a crude sulfonic acid are reduced substantially or, if desired, completely by treatment with hydrogen sulfide or materials affording hydrogen sulfide under the treating conditions, for example hydrogen polysulfides such as H252, H2S3, H285, metal sulfides such as CaS, CaSz, NazS, etc. The reducing treatment of the crude sulfonic acid with hydrogen sulfide may be eifected at temperatures between about C. and about 150 C. One of the principal determinants of the extent of reaction is the molar ratio of hydrogen sulfide to sulfuric acid and other oxidizing impurities contained in the sulfonic acid. Although I do not choose to be bound by any theory of reaction it appears that the following equation represents the predominating reaction which occurs in my process upon contact of hydrogen sulfide with sulfuric acid contained as an impurity in a sulfonic acid:

3H2S H2SO4 41120 43 It is desirable to employ at least 1 mol of H28, preferably 3, or even more, for example, up to about mols of HZS per mol of oxidizing impurity, particularly H2804, contained in the sulfonic acid being treated in accordance with this invention. Depending upon the extent of desulfation of the crude sulfonic acid it is desired to achieve, the reaction temperature, and the H2S1H2SO4 ratio, the reaction period may be varied from about one-half to about 24 hours.

Preferably, although not necessarily, the reaction of hydrogen sulfide with oxidizing impurities contained in a sulfonic acid is conducted at temperatures between about 100 C. and 120 C. so that the sulfur formed in the reaction separates as a liquid or in relatively coarse form. Digestion of the reaction mixture for about 8 to 24 hours at about room temperature after the H25 treatment increases the filterability of the sulfur produced in the reaction. After the reaction, it is desirable to blow a stream 0)? air or other inert gas, such as nitrogen, carbon dioxide, methane or the like through the reaction mixture to remove the water produced during the reaction of hydrogen sulfide with the sulfuric acid. Upon allowing the resultant mixture to cool and stand for several hours the residual sulfur crystallizes out as a coarse crystal mass which is readily removed by decantation, filtration, centrifuging or the like.

The following examples will serve to illustrate the nature of my invention; it should be understood that they are not adduced for the purpose of unnecessarily limiting the scope of the present invention.

5 precipitate in the reaction mixture.

Example 1 Hydrogen sulfide gas was passed through a mixture of crude C1-C4 alkanesulfonic acids at 30 C. After a few minutes, sulfur began to The acid was then rapidly heated to 112 C. and the introduction of hydrogen sulfide Was continued for 30 minutes. The introduction of hydrogen sulfide was then discontinued and the acid allowed to cool. Liquid sulfur was observed in the hot acid mixture; on cooling overnight a heavy additional crop of crystals separated. The color of the alkanesulfonic acid was substantially unaffected by the hydrogen sulfide treatment. Analyses of the alkanesulfonic mixture before and after reaction were as follows:

Crude Refined acid acid Sulfonic acids, weight percent 93. 2 95.0 H2304, Weight percent 2. 4 O.

Example 2 alkanesulfonic acids:

Crude H S-trcated Acid Acid 0. 3 93. 8 111 111-114 2. 8 0. 00 E 0, Perccnt 3.4 7.3 Ash, Percent 0. 015

45 As has been pointed out above, low pressure or so-called vacuum distillation is an important step in the purification of relatively volatile crude sulfonic acids, particularly crude alkanesulfonic acids having between about 1 and 5 carbon atoms,

inclusive, in the alkyl group. Vacuum distillation of a crude sulfonic acid serves to dehydrate the acid, to remove color bodies and, to some extent, to reduce its sulfuric acid content. However, attempts at vacuum distillation of the above-mentioned alkanesulfonic acids have been of the alkanesulfonic acids containing oxidizing impurities, particularly sulfuric acid, has a characteristic temperature above which it freely and rapidly evolves gases. which interfere with the low pressure distillation of the acid. This characteristic temperature I call the critical gas evolution temperature (C. G. E. T.) Thus crude technical ethanesulfonic acid containing about 1.5 percent of sulfuric acid was observed to have a C. G. E. T. of 90 C. and a mixed crude C1-C4 alkanesulfonic acid containing 2.4 percent of sulfuric acid was found to have a C. G. E. T. of '78 C. If distillation of either of these crude acids is attempted, it is'found that no vacuum pump will maintainthe desired reduced pressure if the distillation temperature is allowed to exceed the C. G. E. T. of the acid being distilled. It is obvious therefore, that the C. G. E. T. of the material being distilled imposes a serious limitation on the distillation rate which may be achieved and that any means of substantially increasing the C. G. E. T. of an alkanesulfonic acid or mixture of alkanesulfonic acids will permit a substantial improvement in its low pressure or vacuum distillation.

The following example illustrates my discovery of "the fact that hydrogen sulfide treatment of a sulfonic acid containing oxidizing impurities increases its C. G. E T. substantially.

Example 3 A'crude technical ethanesulfonic acid (1000 00.). having an average molecular weight of 110 and containing 95% sulfonic acid and 1.5 weight per cent sulfuric acid was heated to 240 F. and H25 was bubbled slowly through it for three hours, during which the reaction temperature varied from 228 F. to 248 F., to effect desulfation. The reaction mixture was allowed tocool overnight to room temperature, depositing crystalline sulfur in the reaction vessel. Sulfur was removed by filtration. The crude and the Has-treated acid were then distilled at low pressure. The average'distillation temperature of the crude sulfonic acid was 88 C. and of the HzS-treated acid was 95 C. The distillation pressures varied somewhat but averaged about 0.06 mm. of mercury. In the following table are analytical data concerning the distillation characteristics of the crude and HzS-treated acid.

Cr d

u e His-Treated CZHSSOZH 9 topping step 4.

(8 hrs. more).

Time to de-gas, hrs

Charge to distillation, con. 80 Total Distillation Time,

hrs. Max. distillation. rate,

' cc./hr. Avg. distillation rate,

About 105.

It will be noted that not only was the length of the expensive, time-consuming de-gasing step greatly reduced, but also the C. G. E. T. was raised at least 0., thereby permitting almost a doubled rate of distillation.

4 In general, while I may employ pressures up to about 10 mm., I prefer to employ pressures not in excess of about 1 mm. and usually 0.01-0.1 mm, of mercury in the distillation of sulfonic acids, particularly alkanesulfonic acids having 1 to 5 carbon atoms, inclusive, in the alkyl group.

While the combination of hydrogen sulfide treatment and low pressure distillation to purify sulfonic acids has been described above with particular reference to alkanesulfonic acids having 1 to 5 carbon atoms, inclusive, in the alkyl group, it is obvious that it may likewise be applied to other volatile alkaneor cycloalkane-sulfonic acids which may be distilled at pressures below about 0.01 mm. of mercury without excessive crude alkanesulfonic acid at a reaction temperature between about 0 C. and about C. with hydrogen sulfide in an amount suflicient to reduce a substantial proportion of said sulfuric acid to produce sulfur and separating said sulfur from the reaction mixture.

2. A process of purifying a crude alkanesulfonic acid having 1 to 5 carbon atoms, inclusive, in the alkyl group, said crude acid containing sulfuric acid as an impurity, which process comprises contacting said crude alkanesulfonic acid at a reaction temperature between about 0 C. and about 150 C. with hydrogen sulfide in an amount sufiicient to reduce a substantial proportion of said sulfuric acid to produce sulfur and separating said sulfur from the reaction mixture.

3. A process for purifying a crude alkanesulfonic acid containing sulfuric acid as an impurity, which process comprises contacting said crude alkanesulfonic acid at a temperature between about 0 C. and about 150 C. with hydrogen sulfide in an amount at least equimolar with respect to the amount of sulfuric acid contained in said crude alkanesulfonic acid, and separating sulfur, resulting from the reaction, from the reaction mixture.

4. A process of purifying a crude alkanesulfonic acid having 1 to 5 carbon atoms, inclusive, in the alkyl group, said crude acid containing sulfuric acid as an impurity, which process comprises contacting said crude alkanesulfonic acid at a temperature between about 0 C. and about 150 C. with'hydrogen sulfide in an amount at least equimolar with respect to the amount of sulfuric acid contained in said crude alkanesulfonic acid, and separating sulfur, resulting from the reaction, from the'reaction mixture.

5. A process for purifying a crude alkanesulfonic acid containing sulfuric acid as an impurity, which process comprises contacting said crude alkanesulfonic acid at a temperature between about 0 C. and about 150 C. with hydrogen sulfide in an amount at least trimolar with respect to the amount of sulfuric acid contained in said crude alkanesulfonic acid, and separating sulfur, resulting from the reaction, from the reaction mixture.

6. A process of purifying a crude alkanesulfonic acid having 1 to 5 carbon atoms, inclusive, in the alkyl group, said crude acid containing sulfuric acid as an impurity, which process com prises contacting said crude alkanesulfonic acid at a temperature between about 0 C. and about 150 C.'with hydrogen sulfide in an amount at least trimolar with respect to the amount of sulfuric acid contained in said crude alkanesulfonic acid, and separating sulfur, resulting from the reaction, from the reaction mixture.

'7. A process for purifying a distillable crude alkanesulfonic acid containing sulfuric acid 'as an impurity, which process comprises contacting said alkanesulfonic acid at a temperature between about 0 C. and about 150 C. with hydrogen sulfide in an amount sufiicient to reduce a substantial proportion of said sulfuric acid, thereafter separating solids produced by the reaction from the resultant reaction mixture, and subjecting the liquid reaction products thus obtained 7. to distillation at apressure not-in excess of about 10 mrn.ofmercury.

8. A process of purifying a crude alkanesulionic acid having 1 to 5 carbon atoms, inclusive, in the alkyl group, said crude acid containing sulfuric acid as an impurity. which process comprises contacting said alkanesulfonicacid at a temperature between about C. and about 150 C. with hydrogen sulfide in an amount sufficient to reduce a substantial proportion of said sulfuric acid, thereafter separating solids produced by the reaction from the, resultant reaction mixture, and subjecting the liquid reaction products thusv obtained to distillation at a pressure not in excessof about 10 mm. of mercury.

9. A process for purifying a distillable crude alkanesulfonic acid containing sulfuric acid as an impurity, which process comprises contacting said alkanesulfonic acid at a temperature between 0 C. and about 150 C. with hydrogen sulfide in an amount sufficient to reduce a substantial proportion of said sulfuric acid, thereafter separating solids produced by the reaction from the resultant reaction mixture, and subjecting the liquid reaction products thus obtained to distillation at a temperature in excess of the criticalgas evolution temperature of said crude alkanesulfonic acid.

10. A process of purifying a crude alkanesulfonic acid having 1 to carbon atoms, inclusive, in the alkyl group, said crude acid containing sulfuric acid as an impurity, which process comprises contacting said alkanesulfonic acid at a temperature between about 0 C. and about 150 C. with hydrogen sulfide in an amount sufiicient r an impurity, which process comprises contacting said alkanesulfonic acid at a temperature between about 0 C. and about 150 C. with hydrogen sulfide in an amount suiiicient to reduce a substantial proportion of said sulfuric acid, thereafter separating solids produced by the reaction :2

from the resultant reaction mixture, and subjecting the liquid reaction products thus obtained to distillation at a temperature in excess of the critical gas evolution temperature ofsaid crude alkanesulfonic acid and a pressure not exceeding about mm. of mercury.

12. A process of purifying a crude alkanesulfonic acid having 1 to 5 carbon atoms, inclusive, in; the alkyl group, said crude acid containing sulfuric acid as an impurity, which process compriises contacting said sulfonic acid at a temperature between about 0 C. and about 150 C. with hydrogen sulfide in an amount sumcient to reduce a substantial proportion of said sulfuric acid, thereafter separating solids produced by the reac- 8 tion from the resultant reaction mixture, and subjecting the liquid reaction products thus obtained todistillation at a temperature inv excess of the critical gas evolution temperature of said crude sulfonic acid and a pressure not exceeding about 10 mm. of mercury.

13. A process for purifyin a crude alkanesulfonic acid having 1 to 5 carbon atoms, inclusive, in the alkyl group, the concentration of said alkanesulfonic acid being between about and about percent, the concentration of sulfuric acid in said alkanesulfonic acid being between about 1 and about 5 percent, which process comprises contacting said alkanesulfonic acid at a temperature between about 0 C. and about 150 C. with hydrogen sulfide in an amount sufficient to reduce a substantial proportion of said sulfuric acid, thereafter separating solids produced by the reaction from the resultant reaction mixture, and subjecting the liquid reaction products thus obtained to distillation at a temperature in excess of the critical gas evolution temperature of said crude sulfonic acid and a pressure not exceeding about 10 mm. of mercury.

14. A process for purifying a crude alkanesuh ionic acid having 1 to 5 carbon atoms, inclusive, in the alkyl group, the concentration of said alkanesulfonicacid being between about 80 and about 95 percent, the concentration of sulfuric acid in said alkanesulfonic acid being between about 1 and about 5 percent, which process comprises contacting said alkanesulfonic acid at a temperature between about C. and about C. with hydrogen sulfide in an amount sufficient to reduce a. substantial proportion of said sulfuric acid, thereafter separating solids produced by the reaction from the resultant reaction mixture, andv subjecting the liquid reaction products thus obtained to distillation at a temperature in excess of the critical gas evolution temperature of said crude sulfonic acid and a pressure not exceeding about 10 mm. of mercury.

15. A process for purifying a crude alkanesulionic acid containing sulfuric acid as an impurity, which process comprises contacting said crude alkanesulfonic acid at a reaction temperature between about 100 C. and about 120 C. with hydrogen sulfide in an amount sufiicient to reduce a substantial proportion of said sulfuric acid to produce sulfur and separating said sulfur from the reaction mixture.

16. A process for purifying a crude alkanesulfonic acid having 1 to 5 carbon atoms, inclusive, in the alkyl group, said crude alkanesulfonic acid containing sulfuric acid as an impurity, which process comprises contacting said crude alkanesulfonic acid at a reaction temperature between about 100 C. and about 120 C. with hydrogen sulfide in an amount sufficient to reduce a substantial proportion of said sulfuric acid to produce sulfur and separating said sulfur from the reaction mixture.

WAYNE A. PROELL.

No references cited. 

1. A PROCESS FOR PURIFYING A CRUDE ALKANESULFONIC ACID CONTAINING SULFURIC ACID AS AN IMPURITY, WHICH PROCESS COMPRISES CONTACTING SAID CRUDE ALKANESULFONIC ACID AT A REACTION TEMPERATURE BETWEEN ABOUT 0*C. AND ABOUT 150*C. WITH HYDROGEN SULFIDE IN AN AMOUNT SUFFICIENT TO REDUCE A SUBSTANTIAL PROPORTION OF SAID SULFURIC ACID TO PRODUCE SULFUR AND SEPARATING SAID SULFUR FROM THE REACTION MIXTURE. 